I had the same thing happen on my '91. I didn't want to spend food money on an alternator so I took it apart and replaced the regulator (after ruling out everything else, of course). If you can solder and have a good hot soldering iron, a multimeter and a test light, it's not too hard to do, and it only cost $34.00. If the truck is your daily driver you may want to put in a new alternator. With key on / engine off, does your battery light in the dash come on? Often times when the battery light never comes on w/ KOEO, it's an indication that the regulator is bad.